1. Field of the Invention
This invention relates to a method and an apparatus for removing flash of polymeric molded products.
2. Description of the Related Art
In the art of injecting synthetic polymers into dies to make molded products, the molded products taken away from the dies, in general, undesirably have flash. Since the dies are assembled to give the die matching surface, the polymers may enter into the die matching surface and solidify there to make flash.
Furthermore. there are specific methods even positively allowing the flash to be produced. For example, in the case of molding foam polyurethane products, the gap at the die matching surface may be slightly enlarged to allow air in the dies to easily escape through the gap.
Referring to FIGS. 27 and 28 showing the related art, a mandrel 202 is located in insert dies (not shown); foam polyurethane is injected into the dies; the solidified polymeric molded product is taken away from the dies to obtain a steering wheel 205 (called simply "ring" hereafter) the mandrel 202 of which is covered with armoring material 201.
During the molding, burr 203 is produced at the inner and outer peripheries of the ring 205. Furthermore, since the molten polymer is injected into the dies generallY through a polymer injection path called a gate, the ring 205 is provided with a solidified polymeric substance 204 set in the injection path (called solidified gate hereafter) as the dies are cooled.
Since the burr 203 is useless for the ring 205, it is usually cut and removed from the ring 205. Of course, the solidified gate 204 is also removed.
Heretofore, the burr removing operation for the burr 203 has been carried out manually using a cutter.
However, the manual burr removing operation has the following problems: the removal leaves an even trace; a part of the product other than the burr is often removed resulting in inferior goods; and the work efficiency is poor.
Under the circumstances, a motor-driven flash removing operation may be considered in which a cutter is installed on the rotary shaft of a motor; the motor is operated by a robot; and the cutter is applied to the flash of the polymeric molded product to remove it.
The direct performance of this motor-driving method can cut and remove the flash, but it suffers from the following problems: excessive removal can occur thus moving a part of product other than the burr; or insufficient removal can occur leaving a part of the flash, thus lowering the commercial value of the products.
Furthermore, soft polymeric molded products and foam products such as polyurethane and rubber, in practice, have at their outer surfaces undulation within tolerance because of their molding distortion. In this case, the above problems would become more significant unless the cutter is moved to follow the undulation.
Accordingly, burr removal by mechanical means having the function of simple cutter rotation has not been in practical use.
On the other hand, using the usual reamer would be considered for the flash removing operation.
The reamer used for this flash removing operation is, as shown in FIG. 29, the very same reamer 206 as for metallic materials. Using this reamer 206, however the blades 207 often invade a part of the product unless careful operation is performed, resulting in inferior goods. Thus, this operation requires high skill and great care.
Furthermore, the reamer 206 defines grooves 208 of V-shaped cross sections between the blades 207; the bottom of the groove 208 is provided with a crack-preventing groove 209 of circular cross section. The removed flash can easily be collected in the grooves 209, so that some cases require another operation to take away the collected flash from the grooves 209.
In addition to the above problems, the flash removing operation by the mechanical means would suffer from another problem that different works to be processed such as different polymeric molded products have to be supported and fixed by appropriate different jigs.
Namely, the works tend to have a great deal of variety in shape because of the use of the small-amount multiproduct production system in recent years, so that more often works of the same kind have the structural details of varying shapes. Therefore, in processing the works, jigs have to be replaced by other ones for different works having different detailed structures.
Such replacement of jigs would cause replacement of associated devices, for example cutting tools, requiring much labor. Using the incorrect cutting tools, would result in production of inferior goods.